Base station and method for receiving control information

ABSTRACT

Disclosed are an encoding ratio setting method and a radio communication device which can avoid encoding of control information at an encoding ratio lower than necessary and suppress lowering of the transmission efficiency of the control information. In the device, an encoding ratio setting unit ( 122 ) sets the encoding ratio R′ control  of the control information which is time-multiplexed with user data, according to the encoding ratio R data  of the user data, ΔPUSCHoffset as the PUSCH offset of each control information, and ΔRANKoffset as the rank offset based on the rank value of the data channel using Expression (1). 
     
       
         
           
             
               
                 
                   
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     Where ┌x┐ is an integer not greater than x, and max(x,y) is the greater one among X and Y.

TECHNICAL FIELD

The present invention relates to a coding rate setting method and aradio communication apparatus used for a radio communication systemusing adaptive modulation and the multiple input multiple output (MIMO)technology.

BACKGROUND ART

For an uplink channel of 3rd generation partnership project radio accessnetwork long term evolution (3GPP RAN LTE, hereinafter referred to as“LTE”), single-carrier transmission is adapted to achieve a low peak toaverage power ratio (PAPR).

Further, for an LTE uplink channel, to achieve high throughput, adaptivemodulation (AMC: adaptive modulation and coding) is used so as to selectthe modulation and coding scheme (MCS) pattern for each user dependingon the channel quality indicator (CQI) of each user.

Further, introduction of the MIMO system is being considered to achievehigher transmission rate and to further improve the efficiency of use offrequency. Introduction of a rank transmission technique is alsoconsidered such as rank adaptation with which the rank indication (thenumber of rank) is adaptively switched depending on the status of aspatial propagation path to further improve transmission rate.

Under these circumstances, an agreement is made to time-multiplexcontrol information and user data using the physical uplink sharedchannel (PUSCH) of the same subframe so as to maintain low PAPR evenwhen both control information and user data are transmitted at the sametime in an LTE uplink channel (see Non-Patent Literature 1).

The number of coded symbols, Q′, of control information to bemultiplexed with user data is set based on equation 1.

$\begin{matrix}{\mspace{79mu} \lbrack 1\rbrack} & \; \\{\mspace{31mu} {Q^{\prime} = {{\min\left( {\left\lceil \frac{O}{10^{\frac{- \Delta_{offset}^{PUSCH}}{10}}.R_{data}} \right\rceil,{4 \cdot M_{sc}}} \right)} = {\min \left( {{Q\; 1},{Q\; 2}} \right)}}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where ┌x┐ is an integer not greater than x, and min(x,y) is the value ofthe smaller one of x and y.

In equation 1, M_(sc) is the number of subcarriers per PUSCH subframe,and ΔPUSCIHoffset is a PUSCH offset which varies per control informationsuch as ACK/NACK, rank indicator (RI), or CQI. ΔPUSCHoffset is reportedfrom a higher layer (see Non-Patent Literature 1).

O is the number of control information bits, and R_(data) is representedby equation 2.

$\begin{matrix}\lbrack 2\rbrack & \; \\{R_{data} = \frac{\sum\limits_{r = 0}^{C - 1}K_{r}}{M_{sc} \cdot N_{symb}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

In equation 2, K is the number of bits on r-th block, C is the number ofblocks per PUSCH subframe, and N_(symb) is the number of symbols perPUSCH subcarrier. The actual coding rate of user data is obtained bydividing R_(data) in equation 2 by the number of bits per symbol, and isin proportion to R_(data) equation 2. Accordingly, R_(data) in equation2 will be hereinafter referred to as “user data coding rate.”

In equation 1, Q1 is the number of coded symbols of control informationthat is set based on the number of control information bits O, user datacoding rate R_(data), and PUSCH offset ΔPUSCHoffset, per controlinformation. Q2 is the upper limit value of the number of coded symbolsof control information. As shown in equation 1, the number of codedsymbols of control information, Q′, is set by the smaller one of thenumber of symbols Q1 and upper limit value Q2.

Here, equation I is modified to provide equation 3. As is the case withR_(data) in equation 2, the actual coding rate of control information isobtained by dividing R_(control) in equation 3 by the number of bits persymbol, and is in proportion to R_(control) in equation 3. Accordingly,R_(control) in equation 3 will be hereinafter referred to as “controlinformation coding rate (coding rate of control information).”

$\begin{matrix}{\mspace{79mu} \lbrack 3\rbrack} & \; \\{R_{control} = {\frac{O}{Q^{\prime}} = {{\max\left( {\left\lceil \frac{O}{10^{\frac{- \Delta_{offset}^{PUSCH}}{10}}.R_{data}} \right\rceil,\frac{O}{4 \cdot M_{sc}}} \right)} = {\max \left( {{R\; 1},{R\; 2}} \right)}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

where ┌x┐ is an integer not greater than x, and max(x,y) is the value ofthe greater one of x and y. In equation 3, R1 is the coding rate that isset based on user data coding rate R_(data) and PUSCH offset,ΔPUSCHoffset, per control information. R2 is the lower limit value ofcontrol information coding rate R_(control). As is shown in equation 3,control information coding rate R_(control) is set to the value of thegreater value of coding rate R1 and lower limit value R2. A case will bedescribed below where coding rate R1 is greater than lower limit valueR2, and control information coding rate R_(control) is set as codingrate R1.

In this case, in equation 3, when PUSCH offset ΔPUSCHoffset is greaterthan 0, control information coding rate R_(control) is set lower thanuser data coding rate R_(data). Generally, unlike user data, controlinformation is not retransmitted. Therefore, by setting PUSCH offsetΔPUSCHoffset, to be greater than 0 and using equation 3, it is possibleto lower control information coding rate R_(control) than user datacoding rate R_(data) to enhance the capability of error correction ofcontrol information.

CITATION LIST Non-Patent Literature

-   3GPP TS 36.212 v 8.4.0, “Uplink transport channels and control    information”

SUMMARY OF INVENTION Technical Problem

However, when control information coding rate R_(control) is set simplyby using only user data coding rate R_(data) and PUSCH offsetΔPUSCH_(offset), per control information, there is a possibility thatadaptive modulation is applied depending on a channel quality indicatorof user, and efficiency of control information transmission is decreasedwhen rank indication of a data channel (hereinafter referred to as “dataCH”) in which user data is transmitted, is transmitted.

For example, when rank 2 is applied to a data CH and reception qualityis deteriorated due to interference between streams (inter-streaminterference), in adaptive modulation, user data MCS is lowered and userdata coding rate R_(data) is set lower to prevent the decrease in theefficiency of transmission due to deteriorated reception quality.

In such a case where user data MCS is lowered by adaptive modulation, ifcontrol information coding rate R_(control) is set based on equation 3,control information coding rate R_(control) may be set excessively low.As a result of this, for example, even when the rank indication of acontrol channel (hereinafter referred to as “control CH”), in whichcontrol information is transmitted, is not transmitted, and the controlCH is not subject to the influence of interference between streams,control information is encoded at a lower coding rate to haveexcessively high quality, therefore lowering the efficiency of controlinformation transmission.

In view of the above, it is therefore an object of the present inventionto provide a coding rate setting method and a radio communicationapparatus that can prevent control information from being encoded at anexcessively low coding rate and can suppress the decrease in theefficiency of control information transmission.

Solution to Problem

A coding rate setting method according to the present invention sets auser data coding rate to be adaptively set according to a channelquality indicator of a user as a reference value, corrects the referencevalue based on a type of control information to be time-multiplexed withthe user data and a rank indication of a data channel in which the userdata is transmitted, and

sets the corrected reference value as a control information coding rate.

A radio communication apparatus according to the present inventioncomprises a coding rate obtaining section that sets a user data codingrate to be adaptively set according to a channel quality indicator of auser as a reference value, obtains the reference value corrected basedon a type of control information to be time-multiplexed with the userdata and a rank indication of a data channel in which the user data istransmitted, as a the control information coding rate, and an encodingsection that encodes the control information based on the controlinformation coding rate.

Advantageous Effects of Invention

According to the present invention, it is possible to prevent controlinformation from being encoded at an excessively low coding rate, andsuppress the decrease in the efficiency of control informationtransmission.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a main configuration of a terminalaccording to Embodiment 1 of the present invention;

FIG. 2 is a block diagram showing a main configuration of a coding ratesetting section according to Embodiment 1 of the present invention;

FIG. 3 shows an example of a rank information offset table according toEmbodiment 1 of the present invention;

FIG. 4 shows another example of a rank information offset tableaccording to Embodiment 1 of the present invention;

FIG. 5 is a block diagram showing a main configuration of a terminalaccording to Embodiment 2 of the present invention;

FIG. 6 is a block diagram showing a main configuration of a coding ratesetting section according to Embodiment 2 of the present invention;

FIG. 7 shows an example of a rank information offset table according toEmbodiment 2 of the present invention;

FIG. 8 shows another example of a rank information offset tableaccording to Embodiment 2 of the present invention; and

FIG. 9 shows yet another example of a rank information offset tableaccording to Embodiment 2 of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

Embodiment 1

A case will be described here with the present embodiment where acontrol information coding rate is set by a offset corresponding to arank indication of a data CH in which user data is transmitted, whenadaptive modulation is applied according to a channel quality indicatorof a user. Control information may include ACK/NACK, R1, and CQI, forexample, and is time-multiplexed with user data to be transmitted from aterminal apparatus (hereinafter referred to as “terminal”) to a basestation apparatus (hereinafter referred to as “base station”).

The control information coding rate can be set either at a base stationor at a terminal. A case will be described below where the controlinformation coding rate is set at a terminal.

FIG. 1 is a block diagram showing a main configuration of a terminalaccording to the present embodiment. In FIG. 1, receiving section 110 ofterminal 100 comprises radio receiving section 111, cyclic prefix (CP)removing section 112, fast Fourier transform (FFT) section 113,propagation path estimation section 114, demodulation section 115, anddecoding section 116. Further, in FIG. 1, transmission section 120 ofterminal 100 comprises coding rate setting section 121, coding ratesetting section 122, coding modulation section 123, coding modulationsection 124, channel multiplexing section 125, discrete Fouriertransform-spread-OFDM (DFT-s-OFDM) section 126, CP adding section 127,and radio transmission section 128.

Radio receiving section 111 converts a received signal received via anantenna to a baseband signal, and outputs the baseband signal to CPremoving section 112.

CP removing section 112 removes a cyclic prefix (CP) from the basebandsignal output from radio receiving section 111 and outputs, as a timedomain signal, the baseband signal without a CP to FFT section 113.

FFT section 113 obtains a frequency domain signal by performing a fastFourier transform on the time domain signal output from CP removingsection 112, and outputs the obtained frequency domain signal topropagation path estimation section 114 and demodulation section 115.

Propagation path estimation section 114 estimates the propagation pathenvironment of the received signal by using a pilot signal contained inthe frequency domain signal output from FFT section 113, and outputs theestimation result, which is the estimated propagation path environmentof the received signal, to demodulation section 115.

Demodulation section 115 applies a propagation path compensation withrespect to the frequency domain signal which is output from FFT section113, and from which the pilot signal is removed, based on the estimationresult output from propagation path estimation section 114. Further,demodulation section 115 demodulates the frequency domain signal afterpropagation path compensation based on the same MCS as used at the basestation, i.e. the same modulation scheme and coding rate, etc. to obtaina demodulated signal, and outputs the obtained demodulated signal todecoding section 116.

Decoding section 116 corrects errors with respect to the demodulatedsignal output from demodulation section 115, to obtain a decoded signal.Then, decoding section 116 extracts, from the obtained decoded signal,information such as an information data sequence, the number of bits perblock K_(r), the number of subcarriers per subframe M_(sc), the numberof symbols per subcarrier N_(symb), a PUSCH offset, and a data CH rankindication (the number of a rank for a data CH). Information aboutM_(sc) and N_(symb) are set at favorable values at a base station bybeing adaptively modulated according to the CQI transmitted fromterminal 100. Decoding section 116 outputs the extracted information onK_(r), M_(sc) and N_(symb) to coding rate setting section 121, andoutputs the extracted information on the PUSCH offset and the data CHrank indication to coding rate setting section 122.

Coding rate setting section 121 sets user data coding rate R_(data)based on information on K_(r), M_(sc), and N_(symb) input from decodingsection 116, based on equation 2. Coding rate setting section 121outputs the set user data coding rate R_(data) to coding rate settingsection 122 and coding modulation section 123.

Coding rate setting section 122 sets control information coding rateR′_(control) based on information on user data coding rate R_(data), thePUSCH offset, and the data CH rank indication. The internalconfiguration of coding rate setting section 122 and the method ofsetting control information coding rate R′_(control) will be describedlater. Coding rate setting section 122 outputs the set controlinformation coding rate R′_(control) to coding modulation section 124.

Coding modulation section 123 generates encoded data by encoding theinput user data based on information on user data coding rate R_(data)output from coding rate setting section 121, and generates data CHtransmission data by modulating the generated encoded data. Codingmodulation section 123 outputs the generated data CH transmission datato channel multiplexing section 125.

Coding modulation section 124 generates encoded data by encoding controlinformation based on coding rate R′_(control) output from coding ratesetting section 122, and generates control CH transmission data bymodulating the generated encoded data. Coding modulation section 124outputs the generated control CH transmission data to channelmultiplexing section 125.

Channel multiplexing section 125 time-multiplexes the data CHtransmission data output from coding modulation section 123 and thecontrol CH transmission data output from coding modulation section 124,to generate multiplexed transmission data. Channel multiplexing section125 outputs the multiplexed transmission data to DFT-s-OFDM section 126.

DFT-s-OFDM section 126 obtains a frequency domain signal by performing adiscrete Fourier transform (DFT) on the multiplexed transmission dataoutput from channel multiplexing section 125. DFT-s-OFDM section 126maps the frequency domain signal on a transmission subcarrier, performsan inverse fast Fourier transform (IFFT) on the mapped frequency domainsignal to obtain a transmission data sequence, and outputs the obtainedtransmission data sequence to CP adding section 127.

CP adding section 127 adds a CP to the transmission data sequence outputfrom DFT-s-OFDM section 126 by duplicating the data in the end of aframe and inserting the duplicated data in the head of the frame, ineach frame of the transmission data sequence, and outputs thetransmission data sequence with a CP as the baseband signal, to radiotransmission section 128.

Radio transmission section 128 converts the frequency with respect tothe baseband signal output from CP adding section 127 into radiofrequency bandwidth to obtain a transmission signal, and transmits theobtained transmission signal via an antenna.

FIG. 2 is a block diagram showing an internal configuration of codingrate setting section 122 according to the present embodiment.

Rank information offset obtaining section 1221 stores rank informationoffset table 1222 inside, and obtains rank offset ΔRANKoffset from rankinformation table 1222 corresponding to the data CH rank indication.Rank information offset table 1222 will be explained later. Rankinformation offset obtaining section 1221 outputs the obtained rankoffset ΔRANKoffset to coding rate calculating section 1223.

Coding rate calculating section 1223 sets control information codingrate R′_(control) based on user data coding rate R_(data), PUSCH offsetΔPUSCHoffset and rank offset ΔRANKoffset, corresponding to the data CHrank indication, based on equation 4.

$\begin{matrix}{\mspace{79mu} \lbrack 4\rbrack} & \; \\{R_{control}^{\prime} = {\frac{O}{Q^{\prime}} = {{\max\left( {\frac{O}{\left\lceil \frac{O}{10^{\frac{{- \Delta_{offset}^{PUSCH}} + \Delta_{offset}^{RANK}}{10}} \cdot R_{data}} \right\rceil},\frac{O}{4 \cdot M_{sc}}} \right)} = {\max\left( {{R^{\prime}1},{R^{\prime}2}} \right)}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

where ┌x┐ is an integer not greater than x, and max(x,y) is the value ofthe greater one of x and y.

In equation 4, R′1 is a coding rate that is set based on user datacoding rate R_(data), PUSCH offset per control information which isdefined as ΔPUSCHoffset, and rank offset corresponding to the data CHrank indication which is defined as ΔRANKoffset. R2′ is the lower limitvalue of control information coding rate R′_(control). A case will bedescribed below where coding rate R′1 is greater than lower limit valueR′2, and control information coding rate R_(control) is set as codingrate R′1.

Further, in equation 4, O is the number of control information bits andQ′ is the number of coded symbols of control information. The number ofcoded symbols of control information Q′ is represented by equation 5.

$\begin{matrix}\lbrack 5\rbrack & \; \\{Q^{\prime} = {\min\left( {\frac{O}{\left\lceil \frac{O}{10^{\frac{{- \Delta_{offset}^{PUSCH}} + \Delta_{offset}^{RANK}}{10}} \cdot R_{data}} \right\rceil},\frac{O}{4 \cdot M_{sc}}} \right)}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

where ┌x┐ is an integer not greater than x, and min(x,y) is the value ofthe smaller one of x and y. As is obvious in equation 4, according tothe present embodiment, by correcting user data coding rate R_(data)using PUSCH offset ΔPUSCHoffset, corresponding to a type of controlinformation and rank offset ΔRANKoffset, corresponding to a data CH rankindication, it is possible to set the corrected user data coding rate ascontrol information coding rate R′_(control). In other words, by settingthe user data coding rate R_(data), to be adaptively set according tothe user CQI, as a reference value, and by correcting the referencevalue based on PUSCH offset ΔPUSCHoffset, corresponding to the type ofcontrol information, and rank offset ΔRANKoffset, corresponding to thedata CH rank indication, it is possible to set the corrected referencevalue as control information coding rate R′_(control).

As PUSCH offset ΔPUSCHoffset corresponding to the type of controlinformation, ΔHARQ-ACK is used when control information is HARQ-ACK, ΔRIis used when control information is RI, and ΔCQI is used when controlinformation is CQI, for example. An offset corresponding to the type ofcontrol information such as ΔHARQ-ACK, ΔRI, and ΔCQI is reported from abase station via a higher layer (see Non-Patent Literature 1).

FIG. 3 shows an example of rank information offset table 1222 storedinside the rank information offset obtaining section 1221. According tothe present embodiment, rank information offset table 1222 stores rankoffset, ΔRANKoffset, of a greater value for a data CH rank indication ofa greater value. For example, in rank information offset table 1222 inFIG. 3, rank offsets ΔRANKoffset, are set at from a to z in ascendingorder of data CH rank indications, and ΔRANKoffset values of from a to zare set to satisfy z> . . . >b>a.

As described above, by setting rank offset ΔRANKoffset of a greatervalue for the data CH rank indication of a greater value, it is possibleto correct control information coding rate R′_(control), to be obtainedbased on equation 4, to become higher when the data CH rank indicationis greater.

Generally, the influence of interference between streams becomes greaterwhen a rank indication is greater. Therefore, when a data CH rankindication is large, in adaptive modulation, user data MCS is lowered toensure reception quality. That is, in adaptive modulation, user datacoding rate R_(data) is set lower, when a data CH rank indication isgreater and the influence of interference between streams is greater.

Therefore, in the case where user data coding rate R_(data) is set lowerin adaptive modulation, when the control information coding rate is setusing only PUSCH offset, ΔPUSCHoffset, per control information, based onequation 3, for example, the control information coding rate is setfurther lower than user data coding rate R_(data). Accordingly, there isa possibility that control information is encoded at an excessively lowcoding rate.

In contrast, according to the present embodiment, the controlinformation coding rate is set by equation 4 using rank offset,ΔRANKoffset, of a greater value for a data CH rank indication of agreater value, in addition to an offset per control information. By thismeans, the control information coding rate is corrected higher when thedata CH rank indication is greater, and it is possible to prevent thecontrol information coding rate from being set excessively low. In thisway, according to the present embodiment, it is possible to obtain thecontrol information coding rate by correcting the user data coding rate,based on the difference of the influence of interference between streamsthat a data CH suffers and the influence of interference between streamsthat a control CH suffers.

As described above, according to the present embodiment, coding ratesetting section 122 corrects the value of the user data coding rate tobe adaptively set according to a channel quality indicator of a user,based on the type of control information to be time-multiplexed withuser data and the rank indication of a data CH in which user data istransmitted, and sets the corrected value of the coding rate as thecontrol information coding rate. That is, coding rate setting section122 sets the user data coding rate to be adaptively set according to achannel quality indicator of a user, as a reference value, corrects thereference value based on the type of control information to betime-multiplexed with user data and the rank indication of a data CH inwhich user data is transmitted, and sets the corrected reference valueas the control information coding rate. For example, coding rate settingsection 122 sets control information coding rate R′_(control) to betime-multiplexed with user data, based on user data coding rateR_(data), PUSCH offset ΔPUSCHoffset, per control information, and rankoffset ΔRANKoffset, corresponding to a data CH rank indication, based onequation 4.

In this way, according to the present embodiment, the value of the userdata coding rate is corrected based on the type of control informationand the data CH rank indication, and the corrected value of the codingrate is set as the control information coding rate. By this means, evenwhen the rank indication of a data CH in which user data is transmittedis greater and the user data coding rate is set lower in adaptivemodulation, it is possible to prevent the control information codingrate from being set excessively low and suppress the decrease in theefficiency of control information transmission.

Further, by correcting the control information coding rate to becomehigher when a data CH rank indication is greater, it is possible tocorrect the value of the user data coding rate, based on the differenceof the influence of interference between streams that the data CHsuffers and the influence of interference between streams that a controlCH suffers, so as to set the user data coding rate as the controlinformation coding rate. As a result of this, even when the user datacoding rate is extremely low, it is possible to prevent the controlinformation coding rate from being set excessively low and suppress thedecrease in the efficiency of control information transmission.

A case has been described with the above embodiment as an example whererank information offset obtaining section 1221 stores rank informationoffset table 1222, in which the rank offset is defined separately foreach rank indication, for example, from a to z. Rank information offsetobtaining section 1221, however, may not store rank information offsettable 1222, and may calculate rank offset ΔRANKoffset based on theequation shown as equation 6.

ΔRANKoffset=(rank indication−1)×a(a is a constant)  (Equation 6)

Further, it is not necessary to define the rank offset at a differentvalue for each rank indication, and it is possible to define the samerank offset for a plurality of rank indications. For example, it ispossible to divide data channel rank indications into a plurality ofgroups by comparing the data channel rank indications with apredetermined threshold value, and define a rank offset so that thecontrol information coding rate is set higher when a data CH rankindication in each group is greater. As shown in FIG. 4, for example, itis possible to define all rank offsets at a(a>0) for the rank indicationof 2 or greater.

Embodiment 2

A case has been described with Embodiment 1 where, when a data CH rankindication is transmitted, the control information coding rate is setbased on a rank offset corresponding to the data CH rank indication. Acase will be described here with the present embodiment where, when adata CH rank indication and a control CH rank indication (the number ofa rand for a control CH) are transmitted, the control information codingrate is set based on the rank offset based on the combination of thedata CH rank indication and the control CH rank indication.

FIG. 5 is a block diagram showing a main configuration of a terminalaccording to the present embodiment. In a terminal according to thepresent embodiment in FIG. 5, parts that are the same as in FIG. 1 willbe assigned the same reference numerals as in FIG. 1 and overlappingexplanations will be omitted. In FIG. 5, terminal 100 a is provided withdecoding section 116 a and coding rate setting section 122 a instead ofdecoding section 116 and coding rate setting section 122 in terminal 100in FIG. 1.

As is the case with Embodiment 1, the control information coding ratecan be set either at a base station or at a terminal. A case will bedescribed below where the control information coding rate is set at aterminal.

Decoding section 116 a obtains a decoded signal by correcting errorswith respect to a demodulated signal output from demodulation section115. Then, decoding section 116 a extracts, from the obtained decodedsignal, information including an information data sequence, the numberof bits per block K_(r), the number of subcarriers per subframe M_(sc),the number of symbols per subcarrier N_(symb), the PUSCH offset, thedata CH rank indication, and the control CH rank indication.

Decoding section 116 a outputs the extracted information on K_(r),M_(sc), and N_(symb) to coding rate setting section 121, and outputsinformation on the PUSCH offset, the data CH rank indication and thecontrol CH rank indication to coding rate setting section 122 a.

Coding rate setting section 122 a sets control information coding rateR′_(control) based on information on user data coding rate R_(data), thePUSCH offset, and the combination of the data CH rank indication and thecontrol CH rank indication. The internal configuration of coding ratesetting section 122 and the method of setting control information codingrate R′_(control) will be explained later. Coding rate setting section122 a outputs the set control information coding rate R′_(control) tocoding modulation section 124.

FIG. 6 is a block diagram showing an internal configuration of codingrate setting section 122 a according to the present embodiment.

Rank information offset obtaining section 1221 a stores rank informationoffset table 1222 a inside, and obtains a rank offset ΔRANKoffset,corresponding to the combination of the data CH rank indication and thecontrol CH rank indication, from rank information table 1222 a. Rankinformation offset table 1222 a will be explained later. Rankinformation offset obtaining section 1221 a outputs the obtained rankoffset ΔRANKoffset, to coding rate calculating section 1223 a.

Coding rate calculating section 1223 a sets control information codingrate R′_(control) based on user data coding rate R_(data), PUSCH offsetΔPUSCHoffset, and rank offset ΔRANKoffset, corresponding to thecombination of the data CH rank indication and the control CH rankindication, based on equation 4.

FIG. 7 shows an example of rank information offset table 1222 a storedinside the rank information offset obtaining section 1221 a. FIG. 7shows a case where the maximum rank indication is 2. According to thepresent embodiment, rank information offset table 1222 a stores rankoffsets ΔRANKoffset, corresponding to the combinations of a data CH rankindication and a control CH rank indication. The relationship betweenrank offsets ΔRANKoffset and the combinations of a data CH rankindication and a control CH rank indication will be described below.

As shown in case #1 in FIG. 7, when both the data CH rank indication andthe control CH rank indication are 1, both the data CH and the controlCH do not suffer interference between streams. Therefore, when obtainingthe control information coding rate by correcting the user data codingrate, it is not necessary to consider the difference of the influence ofinterference between streams that the data CH suffers and the influenceof interference between streams that the control CH suffers.Accordingly, as shown in case #1, when both the data CH rank indicationand the control CH rank indication are 1, rank offset ΔRANKoffset is setat 0. When rank offset ΔRANKoffset is 0, the control information codingrate coincides with the coding rate that is set based on equation 3.

As shown in case #2 in FIG. 7, when the data CH rank indication is 1 andthe control CH rank indication is 2, only control information suffersreception quality deterioration due to interference between streams. Inthis case, rank offset ΔRANKoffset is set at a (a<0). By settingΔRANKoffset smaller than 0, it is possible to set the controlinformation coding rate obtained based on equation 4 lower than thecontrol information coding rate obtained based on equation 3. By thismeans, it is possible to enhance the capability of error correction ofcontrol in formation.

As shown in case #3 in FIG. 7, when the data CH rank indication is 2 andthe control CH rank indication is 1, only user data suffers receptionquality deterioration due to interference between streams. In this case,rank offset ΔRANKoffset is set at b (b>0). By setting ΔRANKoffsetgreater than 0, it is possible to set the control information codingrate obtained based on equation 4 higher than the control informationcoding rate obtained based on equation 3. By this means, it is possibleto prevent control information from being encoded at an excessively lowcoding rate and suppress the decrease in the efficiency of controlinformation transmission.

As shown in case #4 in FIG. 7, when the data CH rank indication and thecontrol CH rank indication are 2, both the data CH and the control CHsuffer interference between streams. In this case, the influence ofinterference between streams is considered to be approximately equalbetween user data and control information. Accordingly, as shown in case#4, when both the data CH rank indication and the control CH rankindication are 2, the value (c), corresponding to the slight differenceof the influence of interference between streams that the data CHsuffers and the influence of interference between streams that thecontrol CH suffers in the communication status between a base stationand a terminal, is set as rank offset ΔRANKoffset. When the influence ofinterference between streams that a data CH suffers and the influence ofinterference between streams that a control CH suffers are equal, rankoffset ΔRANKoffset may be set at 0, as is the case with case #1.

FIG. 8 shows another example of rank information offset table 1222 astored inside the rank information offset obtaining section 1221 a. FIG.8 shows a case where the maximum rank indication is 4. The relationshipbetween rank offset values ΔRANKoffset and the combinations of a data CHrank indication and a control CH rank indication will be describedbelow. The explanation for cases #1 to 4 in FIG. 8 are the same as forcases #1 to 4 in FIG. 7, therefore the explanation will be omitted.

As shown in cases #5 and 9 in FIG. 8 and as is the case with case #2 inFIG. 7, when the control CH rank indication is greater than the data CHrank indication, control information reception quality deteriorates moreseverely than user data reception quality, due to the difference of theinfluence of interference between streams. In this case, rank offsetΔRANKoffset is set smaller than 0. By setting ΔRANKoffset smaller than0, it is possible to set the control information coding rate obtainedbased on equation 4 lower than the control information coding rateobtained based on equation 3. By this means, it is possible to enhancethe capability of error correction of control information. In this case,for example, when the greater absolute value of rank offset ΔRANKoffsetis set as the data CH rank indication is smaller than the control CHrank indication, the control information coding rate becomes lower asthe data CH rank indication is smaller than the control CH rankindication. Therefore, it is possible to prevent the control informationreception quality from being deteriorated.

As shown in cases #6, 7, and 10-12 in FIG. 8 and as is the case withcase #3 in FIG. 7, when the data CH rank indication is greater than thecontrol CH rank indication, the user data reception quality deterioratesmore severely than the control information reception quality due to thedifference of the influence of interference between streams. In thiscase, rank offset ΔRANKoffset is set greater than 0. By settingΔRANKoffset greater than 0, it is possible to set the controlinformation coding rate obtained based on equation 4 higher than thecontrol information coding rate obtained based on equation 3. By thismeans, it is possible to prevent control information from being encodedat an excessively low coding rate and suppress the decrease in theefficiency of control information transmission. In this case, forexample, when the greater absolute value of rank offset ΔRANKoffset isset as the data CH rank indication is greater than the control CH rankindication, the control information coding rate becomes higher as thedata CH rank indication is greater than the control CH rank indication.As a result of this, it is possible to prevent control information frombeing encoded at an excessively low coding rate and suppress thedecrease in the efficiency of control information transmission.

As shown in cases #8 and 13 in FIG. 8 and as is the case with case #4 inFIG. 7, when the data CH rank indication and the control CH rankindication are equal, the influence of interference between streams thatthe data CH suffers and the influence of interference between streamsthat the control CH suffers are considered to be approximately equal. Inthis case, as shown in case #4, when both the data CH rank indicationand the control CH rank indication are equal, the value (g and l),corresponding to the slight difference of the influence of interferencebetween streams that a data CH suffers and the influence of interferencebetween streams that a control CH suffers in the communication statusbetween a base station and a terminal, is set as rank offsetΔRANKoffset. When the influence of interference between streams that thedata CH and the influence of interference between streams that thecontrol CI suffers are equal, rank offset ΔRANKoffset may be set at 0,as is the case with case #1.

FIG. 9 shows yet another example of rank information offset table 1222 astored inside rank information offset obtaining section 1221 a. In FIG.9, an identical rank offset ΔRANKoffset is defined for a plurality ofcombinations of a data CH rank indication and a control CH rankindication at rank information offset obtaining section 1221 a. Morespecifically, an identical rank offset ΔRANKoffset is set for thecombination where the data CH rank indication and the control CHI rankindication are equal. The relationship between the combinations of adata CH rank indication and a control CHI rank indication and rankoffset ΔRANKoffset will be described below. FIG. 9 shows a case wherethe maximum rank indication is 4, as is the case with FIG. 8.

As shown in case #1 in FIG. 9, when both the data CH rank indication andthe control CH rank indication are 1, both the data CH and the controlCH do not suffer interference between streams. Further, when both thedata CH rank indication and the control CH rank indication are equal andare 2 or greater, the influence of interference between streams that thedata CH suffers and the influence of interference between streams thatthe control CH suffers are considered to be approximately equal.

In this case, when the data CH rank indication and the control CH rankindication are equal, rank offset ΔRANKoffset is set at 0 assuming thatthe influence of interference between streams is equal between the dataCH and the control CH.

As shown in cases #2-6 in FIG. 9, when the data CH rank indication isgreater than the control CH rank indication, the user data receptionquality deteriorates more severely than the control informationreception quality due to the difference of the influence of interferencebetween streams. In this case, rank offset ΔRANKoffset is set greaterthan 0. By setting ΔRANKoffset greater than 0, it is possible to set thecontrol information coding rate obtained based on equation 4 higher thanthe control information coding rate obtained based on equation 3. Bythis means, it is possible to prevent control information from beingencoded at an excessively low coding rate and suppress the decrease inthe efficiency of control information transmission.

In this case, rank offset ΔRANKoffset of a greater value is set when theratio of the data CH rank indication to the control CH rank indication(the data CH rank indication/the control CH rank indication) is greater.For example, in FIG. 9, when the relationship p>n>m>o>q holds, thecontrol information coding rate becomes higher as the data CH rankindication is greater than the control CH rank indication. Accordingly,it is possible to prevent control information from being encoded at anexcessively low coding rate and suppress the decrease in the efficiencyof control information transmission.

As described above, according to the present embodiment, coding ratesetting section 122 a corrects the value of the user data coding rate tobe adaptively set according to a channel quality indicator of a user,based on the type of control information to be time-multiplexed withuser data and the combination of the data CH rank indication and thecontrol CH rank indication, and sets the corrected value of the codingrate as the control information coding rate. That is, coding ratesetting section 122 a sets the user data coding rate to be adaptivelyset according to a channel quality indicator of a user as a referencevalue, corrects the reference value based on the type of controlinformation to be time-multiplexed with user data and the combination ofthe data CH rank indication and the control CH rank indication, and setsthe corrected reference value as the control information coding rate.For example, control information coding rate, R′_(control), to betime-multiplexed with user data is set based on user data coding rateR_(data). PUSCH offset ΔPUSCHoffset per control information, and rankoffset, ΔRANKoffset, corresponding to the combination of the data CHrank indication and the control CH rank indication, based on equation 4.

Further, by correcting the control information coding rate to be higherwhen the data CH rank indication is greater than the control CH rankindication, it is possible to correct the user data coding rate based onthe difference of the influence of interference between streams that adata CH suffers and the influence of interference between streams that acontrol CH suffers, and set the control information coding rate. As aresult of this, even when the user data coding rate is low, it ispossible to prevent the control information coding rate from being setexcessively low and suppress the decrease in the efficiency of controlinformation transmission.

Although cases have been described above as examples where the controlinformation coding rate is set at a terminal, the present invention isby no means limited to this, and it is equally possible that a basestation sets the control information coding rate and reports the setcontrol information coding rate to a terminal, so that the terminal canobtain the reported control information coding rate.

Further, it is also possible that a base station sets rank offsetΔRANKoffset instead of the control information coding rate, and reportthe set rank offset ΔRANKoffset to a terminal so that the terminal canobtain the control information coding rate using the reported rankoffset ΔRANKoffset.

Further, it is also possible that a base station reports a rankinformation offset table to a terminal via a higher layer.

Further, the present invention is not limited to a data CH and a controlCH, and is also applicable to other two channels having the differentreception qualities required for the present invention.

Although cases have been described with the above embodiment as exampleswhere the present invention is configured by hardware, the presentinvention can also be realized by software in combination with hardware.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. LSI is adopted here butthis may also be referred to as “IC”, “system LSI”, “super LSI”, or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmablefield programmable gate array (FPGA) or a reconfigurable processor whereconnections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology ispossible, for example.

The disclosure of Japanese Patent Application No. 2008-307658, filed onDec. 2, 2008, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is useful as a coding rate setting method and aradio communication apparatus used for the radio communication systemusing adaptive modulation and MIMO technology.

REFERENCE SIGNS LIST

-   100, 100 a Terminal-   110 Receiving section-   111 Radio receiving section-   112 CP removing section-   113 FFT section-   114 Propagation path estimation section-   115 Demodulation section-   116, 116 a Decoding section-   120 Transmission section-   121, 122, 122 a Coding rate setting section-   123, 124 Coding modulation section-   125 Channel multiplexing section-   126 DFT-s-OFDM section-   127 CP adding section-   128 Radio transmission section-   1221, 1221 a Rank information offset obtaining section-   1222, 1222 a Rank information offset table-   1223, 1223 a Coding rate calculating section

1. A base station comprising: a transmitter configured to transmit afirst offset and a second offset to a user equipment (UE); and areceiver configured to receive control information that is encoded inaccordance with a coding rate, the coding rate being set based on aoffset value corresponding to one of the first offset and the secondoffset, the first offset being different from the second offset, whereinthe second offset is not used in a case when a rank indicator is
 1. 2.The base station according to claim 1, wherein the coding rate is setdepending on a type of the control information.
 3. The base stationaccording to claim 3, wherein the type of the control information is oneof a hybrid automatic repeat-request acknowledgement (HARQ-ACK), therank indicator, and a channel quality indicator (CQI).
 4. The basestation according to claim 1, wherein the first offset is used in a casewhen the rank indicator is
 1. 5. The base station according to claim 1,wherein the second offset is used in a case only when the rank indicatoris greater than
 1. 6. The base station according to claim 1, wherein thefirst offset is used in a case when the rank indicator is 1, and thesecond offset is used in a case only when the rank indicator is greaterthan
 1. 7. A method for receiving control information performed by abase station, the method comprising: transmitting a first offset and asecond offset to a user equipment (UE); and receiving controlinformation that is encoded in accordance with a coding rate, the codingrate being set based on a offset value corresponding to one of the firstoffset and the second offset, the first offset being different from thesecond offset, wherein the second offset is not used in a case when arank indicator is
 1. 8. The method according to claim 7, wherein thecoding rate is set depending on a type of the control information. 9.The method according to claim 8, wherein the type of the controlinformation is one of a hybrid automatic repeat-request acknowledgement(HARQ-ACK), the rank indicator, and a channel quality indicator (CQI).10. The method according to claim 7, wherein the first offset is used ina case when the rank indicator is
 1. 11. The method according to claim7, wherein the second offset is used in a case only when the rankindicator is greater than
 1. 12. The method according to claim 7,wherein the first offset is used in a case when the rank indicator is 1,and the second offset is used in a case only when the rank indicator isgreater than
 1. 13. A base station comprising: a transmitter configuredto transmit a first offset and a second offset to a user equipment (UE);and a receiver configured to receive control information that is encodedin accordance with a coding rate, the coding rate being set based on aoffset value corresponding to one of the first offset and the secondoffset, the first offset being different from the second offset, whereinthe one of the first offset and the second offset is selected based on arank indicator.
 14. The base station according to claim 13, wherein thecoding rate is set depending on a type of the control information. 15.The base station according to claim 14, wherein the type of the controlinformation is one of a hybrid automatic repeat-request acknowledgement(HARQ-ACK), the rank indicator, and a channel quality indicator (CQI).16. The base station according to claim 13, wherein the first offset isused in a case when the rank indicator is
 1. 17. The base stationaccording to claim 13, wherein the second offset is used in a case onlywhen the rank indicator is greater than
 1. 18. The base stationaccording to claim 13, wherein the first offset is used in a case whenthe rank indicator is 1, and the second offset is used in a case onlywhen the rank indicator is greater than 1.